1. Field of the Invention
This invention relates generally to improvements in a forging method and system accomplishing warm or hot forging, and more particularly to such a forging method and system of a so-called inline cutting type wherein a cutting operation for a heated elongate bar material is made immediately before forging in a forging line.
2. Description of the Prior Art
A forging system of the above-mentioned type has been proposed and put into practical use as disclosed, for example, in "The 12th International Forging Congress Report", page 205, titled "Forging" and published on Jul. 31, 1962 by All Japan Forging Industrial Association. In this forging system, elongate bar materials stocked in a stock area or a return area are fed to an induction heating apparatus to be heated. The thus heated bar material is moved out from the heating apparatus bit by bit to be fed to a billet shear adjacent the heating apparatus. The billet shear cuts the bar material into billet materials having a predetermined length. The thus formed billet materials are fed to a forging press to be subjected to a die-forging.
The return area is provided to stock therein the bar materials which have been once heated by the induction heating apparatus and returned without being cut by the billet shear. For example, in case a trouble arises in the forging press on the downstream side in a forging line, the cutting operation of the billet shear is immediately interrupted, and all the bar materials (including one in the course of cutting) within the induction heating apparatus are returned to the return area. Within the induction heating apparatus, a plurality of the bar materials are usually aligned in a line. The bar materials returned to the return area are allowed to stand to be cooled to ordinary temperature and then reused together with the bar materials in the stock area.
However, drawbacks have been encountered in such a conventional forging system, as discussed below. Since the forging system is such arranged that all the bar materials (including one in the course of cutting) within the induction heating apparatus are returned to the return area immediately upon occurrence of the trouble on the downstream side of the induction heating apparatus, a variety of bar materials different in length are unavoidably mixed and present in the return area after several troubles have continuously occurred. Accordingly, for example, in case of suspending the bar materials in the return area and transferring them to a required place by using an overhead travelling crane and wires, a wire-binding or wire-applying operation for the bar materials of different length is very difficult, thereby making it difficult to handle the bar materials as a bundle with the overhead travelling crane.
The above-discussed transferring operation for the bar materials is carried out, for example, when the return area has been filled with the bar materials or when an initial setup of the forging process is changed. Particularly at the initial setup changing, it is required to once transfer all the bar materials in the return area to a separate area in order to feed new bar materials thereby preventing foreign materials from being mixed with the new bar materials. Thus, such a transferring operation is necessarily carried out at the initial setup changing.
Otherwise, it has been proposed to carry out a standby operation of the induction heating apparatus, as another measure in case of trouble arising in the downstream side step or apparatus. In this standby operation, the bar materials are maintained within the induction heating apparatus in such a manner that the bar materials make their reciprocating movement in the feed direction of the bar materials so that the bar materials are kept within a predetermined temperature range. Thus, in the standby operation, the materials within the induction heating apparatus are returned to the return area immediately when any trouble arises in the downstream side step or apparatus.
However, with this type of standby operation, the standby operation of the induction heating apparatus is continued as long as the trouble in the downstream side step or apparatus is solved or restored. Additionally, each of the bar materials B within the induction heating apparatus makes its reciprocating movement within a particular heater region of the induction heating apparatus, dissimilarly to its movement during a normal operation, and therefore a temperature difference becomes large throughout the length of each bar material so that excessive heat is applied to a particular part of the bar material. As a result, the structure of part of the bar material is unavoidably changed or deteriorated, thereby making it impossible to use the bar material as a forging material.
For example, in the case of a hot forging, an allowable limit time for the standby operation is within 5 minutes on the assumption that the optimum heating temperature for the bar materials within the induction heating apparatus is 1230.degree. C..+-.25.degree. C. Similarly, the allowable limit time is within 20 minutes on the assumption that the optimum heating temperature is 1230.degree. C..+-.35.degree. C. Accordingly, if the standby operation is continued over the above allowable limit time, the bar materials heated at a temperature outside the optimum heating temperature are unavoidably fed to the dies of the forging press.